Method of forming in place a gelled suspension explosive

ABSTRACT

THE METHOD OF FORMING IN PLACE A STABLE, GELLED SUSPENSION EXPLOSIVE COMPOSITION AS DISCLOSED IN U.S. PAT. 3,409,486 IS IMPROVED BY REGULATING THE PH OF THE COMPOSITION TO A VALUE BETWEEN 4 AND 6 AND INJECTING INTO THE EXIT STREAM FROM THE PUMP AN AQUEOUS SOLUTION OF ZIRCONIUM SULFATE, ALUMINUM SULFATE AND CHROMIC ACID TO YIELD A TOUGHER, MORE WATER RESISTANT GEL.

3,676,236 Patented July 11, 1972 ABSTRACT OF THE DISCLOSURE The method of forming in place a stable, gelled suspension explosive composition as disclosed in US. Pat. 3,409,486 is improved by regulating the pH of the composition to a value between 4 and 6 and injecting into the exit stream from the pump an aqueous solution of zirconium sulfate, aluminum sulfate and chromic acid to yield a tougher, more water resistant gel.

DESCRIPTION OF THE INVENTION US. Pat. 3,409,486 discloses a method of formingin place a stable gelled suspension explosive by pumping into a hole an aqueous slurry comprising:

(a) at least weight percent water,

(b) at least 40 weight percent ammonium nitrate,

(c) at least 0.5 weight percent finely divided solid fuel,

(d) at least 1 weight percent dissolved hexamethylenetetramine, sufficient to improve sensitivity, and

(e) at least 1 weight percent ammonium perchlorate, sufficient to stabilize the composition against variation of sensitivity with changing temperature, followed by injecting a gelling agent into the exit stream from the pump.

The aforementioned patent is directed to problems which arise from variations in temperature conditions, particu larly during severe winters. In very cold weather, gelled suspension explosives become very difficult to pump and the sensitivity may decline with falling temperature. The

sensitivity variation problem is solved, as disclosed in the patent, by addition of ammonium perchlorate and the pumping problem was solved by injecting the gelling agent into the exit stream from the pump.

As a gelling agent, the aforementioned patent discloses the use of borax to eifect the well-known instantaneous gelling of a hydroxy-substituted polymer by formation of borate chelate ion cross-links between hydroxy groups of adjacent polymer strands. The borax gelling effect has been known for over a quarter of a century, being remarkable for the instantaneous speed of reaction and certain physical properties of the gels. (See The Chemorheology of Polyvinyl Alcohol-Borate Gels by R. K. Schultz and R. R. Myers, Macromolecules vol. 2, No. 3, pp. 281-285, May June 1969 for a recent discussion of these gels.) Unfortunately for the present purpose, borate gels of this type are eroded rapidly by currents of water which are frequently found in deep drill holes. When substantial time elapses between the placement of theexplosive and the setting off of the charge, deterioration may have occurred because of the presence of water in the hole, so that results are unsatisfactory.

The improvement of the present invention consists of the steps of regulating the pH of the aqueous slurry to a value between 4 and 7 and injecting into the exit stream from the pump a sufficient quantity of an aqueous solution of zirconium sulfate, aluminum sulfate and chromic acid to convert the thickened slurry into a stable, uniform, water-resistant gel.

The present invention is directed to the problem of deterioration of gelled suspension explosives in drill holes into which water has intruded. This is a problem which is unrelated to variation of sensitivity with temperature; therefore the use of ammonium perchlorate in formation of the gel in place is not essential to the method of which this invention is an improvement. The proportions of other ingredients may also be varied considerably without affecting the present method. By way of illustration,

compositions may be pumped and gelled by the present method with varying proportions as listed below:

Ingredients: Proportions Ammonium nitrate 40-80% Sodium nitrate 0-20% Ammonium perchlorate 02% Hexamethylenetetramine 2-8% Nitric acid (42 Baume'), for each 5 parts of hexamethylenetetramine 3 parts At least 0.5 weight percent of a finely divided solid fuel, selected for example from the following:

Particulate aluminum:

Coarse granular 0-15 Fine powder 0-1.7% Gilsonite 06% Water 820% Polysaccharide gum, suflicient to stabili e the suspension.

A typical composition is made according to the following procedure:

Step 1-Base solution preparation. A typical base solution may be a mixture of the components listed below, heated to 90 F. in preparation for the addition of suspended solids. (For a one ton batch of slurry 1280 lbs.

Salt point of the above is 7812 The solution should be kept at a temperature above 80 F., preferably about 90 F. To obtain the desired pH, 48 lb. of 42 Baum nitric acid is added to the base liquor above. The pH will be 5.411 in this specific example. This lies within the preferred range of about 5.0 to 5.8.

Step 2.The above solution is pumped into a ribbon mixer and there is added about 18 lb. of a commercial polysaccharide gum, for example, General Mills 492 type gum thickener. The mixture is allowed to hydrate for approximately 3 minutes.

Step 3.T he required amounts of coarse aluminum and fine aluminum with the balance of ammonium nitrate to make up the 2000 lb. batch is added and the ribbon is turned at the required rate and time to produce the proper mixing and density of final product. If desired, a solid canbonaceous fuel such as gilsonite may also be added. Gilsonite, because of difiiculty of dispersion in hydrated (thickened) mixes, is customarily added to some of the solution in the mixer before the gum is added. Final temperature of the finished slurry is usually about to and the pH is about 5.4.

The slurry product is transferred to bulk pump trucks or support tankers for distribution to blast holes in the field. The final step is pumping the bulk slurry into blast holes at a temperature of about 70 to 80 F. while injecting the crosslinking agent on the downstream side of the pump. The crosslinker converts the slurry from a sol to a water-resistant gel. This step is described below.

Crosslinking may be accomplished for example, by injecting into the exit stream from the slurry pump from 1.5 to 2 percent by weight of the slurry a crosslinking solution of the following composition:

Ingredients: Parts by weight Zirconium sulfate 7.5 Chromic acid 3.0 Aluminum sulfate 3.0

Water, to make 100 parts total.

Water erosion resistance of the gel may be varied by adjusting the zirconium sulfate content. Pliability or toughness of the gel may be adjusted by varying the chromic acid content. The tendency of water in the blast hole to break down the gel by solubility effects, leaching out the nitrates and carrying away the gilsonite and powdered aluminum in suspension is counteracted by the aluminum sulfate. The specifically disclosed crosslinking solution is believed to be about the best compromise for the range of explosive compositions disclosed above. However, it will be understood that for a specific problem situation it may be desirable to increase or decrease water erosion resistance, insolubility or toughness. For this purpose, the composition of the crosslinking solution may be varied within the limits shown below;

Ingredients: Parts by weight Zirconium sulfate 2-15 Chromie acid l- Aluminum sulfate 1-10 Water, to make 100 parts total.

What is claimed is:

1. In the method of forming in place a stable, gelled suspension explosive composition by pumping into a hole an aqueous slurry comprising:

(a) at least 8 weight percent 'water (b) at least 40 Weight percent ammonium nitrate (c) at least 0.5 weight percent finely divided solid fuel,

selected from particulate aluminum and gilsonite (d) at least 1 weight percent dissolved hexamethylenetetramine sufficient to improve sensitivity, and

(e) a stabilizing amount of a water-soluble hydroxysubstituted thickening agent, the improvement consisting of regulating the pH of the aqueous slurry to a value between 4 and 7 and injecting into the exit stream from the pump a sufficient quantity 4 of an aqueous solution of zirconium sulfate, aluminum sulfate and chromic acid to convert the thickened slurry into 'a stable, uniform, water-resistant gel.

2. In the method of forming in place a stable, gelled suspension explosive composition by pumping into a hole an aqueous slurry comprising:

-(a) at least 8 weight percent water (b) at least 40 weight percent ammonium nitrate (c) at least 0.5 weight percent finely divided solid fuel,

selected from particulate aluminum and gilsonite (d) at least 1 weight percent dissolved hexamethylenetetramine suflicient to improve sensitivity (e) at least 1 weight percent ammonium perchlorate,

sufficient to stabilize the composition against variation of sensitivity with changing temperature, and

(f) a stabilizing amount of a Water-soluble hydroxysubstituted thickening agent, the improvement consisting of regulating the pH of the aqueous slurry to a value between 5.0 and 5.8 and injecting into the exit stream from the pump a suflicient quan tity of an aqueous solution of zirconium sulfate, aluminum sulfate and chromic acid to convert the thickened slurry into a stable, uniform, water-resistant gel.

3. The method of claim 2 in which the aqueous slurry is prepared by suspending the undissolved solid ingredients of the composition in an aqueous solution comprising lwater, ammonium nitrate, sodium nit-rate, hexamethylenetetramine, nitric acid and a quantity of a polysaccharide gum suflicient to stabilize the suspension.

References Cited UNITED STATES PATENTS 3,222,232 12/1965 Schwvoyer 14944 X 3,235,423 2/1966 Ferguson 149---44 X 3,282,752 11/1966 Clay et al. 149-44 X 3,303,074 2/1967 Schwoyer 149--44 X 3,465,675 9/1969 Bronstein 149-44 X 3,523,048 8/ 1970 Hopler 149-44 X CARL D. QUIARFORTH, Primary Examiner S. I. LECHERT JR., Assistant Examiner l US. Cl. X.R. 

